During the installation of conventional outdoor lamps, usually it is necessary to directly connect the electric wires pre-positioned at the rear part of the mount base of the lamp and the electric wires pre-positioned in the junction box at user's home by wire caps. In this case, since two hands of installation personnel are busy for the connection of the electric wires, the unfixed lamp will hang in the air during such connection of the electric wires. Hence, the lamps are inconvenient to install.